1. Field of the Invention
The present invention relates generally to microreactor and microfluidic devices and systems, typically devices with at least one characteristic dimension of around a few millimeters or less, and particularly to high throughput, thermally tempered microreactor devices and microfluidic devices.
2. Technical Background
One current focus for microreaction technology is on utilizing the high surface-to-volume ratios possible in small channels—one or more orders of magnitude greater than typical batch reactors—to provide advantages both in chemical lab work and in chemical processing and production.
Devices with very high surface to volume ratios have the capability to provide high heat and mass transfer rates within small volumes. Well-recognized potential advantages include (1) higher productivity and efficiency through higher yield and purity, (2) improved safety through dramatically reduced process volumes, (3) access to new processes, new reactions, or new reaction regimes not otherwise accessible, which may in turn provide even greater yield, purity, or other benefits.
Challenges exist, however, in providing microreaction devices and processes to achieve high-throughput, high-yield, well-controlled performance of fast exothermic or fast endothermic reactions, particularly those that are especially temperature-sensitive. Fast exothermic or fast endothermic reactions can quickly produce or absorb sufficient heat to significantly alter reactant temperatures. If the desired reaction is also particularly temperature-sensitive, the heat generated or absorbed by the reaction typically results in poor or even zero yield, due to poor reaction control allowing undesired or uncontrolled reactions.
Challenges also exist in maintaining local molar ratios at or below desired levels in microreaction environments. Since many reactions are highly sensitive to any excess of one reactant, local buildup of that one reactant to levels above the desirable molar ratio for the reaction can cause unwanted side reactions or follow-on reactions and resulting loss of yield.
Microreaction devices intended for temperature-sensitive fast endothermic or fast exothermic reactions are typically provided with smaller-dimensioned channels, even relative to other microreaction devices, such as on the order of 100 μm or even less, so as to achieve very high surface to volume ratios within the channels. The higher surface to volume ratios provide faster heat transport, allowing generally for improved reaction control and yield relative to larger-dimensioned devices. But decreasing the channel dimensions generally also decreases throughput, particularly if pressure drop is to be kept at reasonable levels.
As a means of compensating for or offsetting this tendency toward decreased throughput in microreaction devices, “external numbering up” or “internal numbering up” or both are employed. External numbering up involves placing multiple separate microreaction devices in parallel, with external fluid distribution equipment to deliver fluids to the devices. Internal numbering up involves including, within a given microreaction device, multiple mixing and/or reaction chambers in parallel. In either case, however, flow balancing becomes critical, and small flow deviations can result in poor reaction control by producing locally imbalanced molar ratios.
Numbering up can also be expensive. External numbering up requires external regulation control systems, which can be a significant expense. In the case of internal numbering up, and in the case of passive external flow splitting, even after careful design of the fluid channels and stringent manufacturing control, sufficiently good flow balance is difficult to achieve in typical devices. Slight chemical or mechanical erosion over the life of the device will alter flow balances and resulting molar ratios, further reducing performance. Thus device lifetime can be shortened, and expenses increased, relative to a device without numbering up, or relative to a device that can achieve higher throughput without numbering up. Further, passive flow dividers designed to produce good flow balances for one reaction or reactant system may not perform well with another reaction or reactant. Internal numbering up can thus narrow the range of application of a given device, requiring an increased number of device types or designs to address a given range of reaction parameters, with associated increased expense.
A microreaction device and method particularly well-suited for economically and reliably achieving higher-throughput, high-yield, well-controlled performance of fast exothermic or fast endothermic reactions, and/or for providing a high degree of local molar ratio control is thus desirable.